4.3BSD-UWisc/lib/learn/eqn/L5.1a

#once #create message
.ND
.EQ
delim $$
.EN
.LP
So far we have carefuly skirted around a potential
problem; maybe you've wondered about it.
Suppose we want to produce an equation that looks
like this:
.EQ
x sup { pi + 1 }
.EN
The superscript is complicated, in that it contains
both a $pi$ and a +1, which has to be separated
from the $pi$ by a blank.
But I already told you that a blank terminates
the superscript.  What's going on?

As the first step to finding out, will the input
equation

  x sup pi + 1

produce the output

  $x sup {pi + 1}$ ?
Answer yes or no.
(You can play with the file "Example" if you like.)
.pl 1
#once #create Example
.LP
.EQ
replace me
.EN
.pl 1
#
#once neqn message | nroff -T$term %s/tinyms -
#copyin
#user
#uncopyin
#match no
#log
#next
5.1b